Abstract:

A method for making a transmission electron microscope (TEM) micro-grid
includes the following steps. A carbon nanotube film and a metallic grid
are provided. The carbon nantoube film is laid on the metallic gird. The
carbon nanotube film with the metallic gird is treated with an organic
solvent. Wherein, the carbon nanotube film includes a plurality of carbon
nanotube bundles substantially arranged at the same direction.

Claims:

1. A method for making a transmission electron microscope micro-grid, the
method comprising:(a) providing a carbon nanotube film and a metallic
grid;(b) laying the carbon nanotube film on the metallic grid; and(c)
treating the carbon nanotube film on the metallic with an organic
solvent.

2. The method as claimed in claim 1, wherein step (a) comprises the steps
of: (a1) providing an array of carbon nantoubes; and (a2) drawing the
carbon nanotube film from the array of carbon nantoubes.

3. The method as claimed in claim 2, wherein the array of carbon nanotubes
is a super-aligned array of carbon nanotubes, and the super-aligned array
of carbon nanotubes is made by the steps of:(a11) providing a
substantially flat and smooth substrate;(a12) forming a catalyst layer on
the substrate;(a13) annealing the substrate with the catalyst layer in
air at a temperature in an approximate range from 700.degree. C. to
900.degree. C. for about 30 to 90 minutes;(a14) heating the substrate
with the catalyst layer at a temperature in an approximate range from
500.degree. C. to 740.degree. C. in a furnace with a protective gas
therein; and(a15) supplying a carbon source gas to the furnace for about
5 to 30 minutes.

4. The method as claimed in claim 1, wherein a material of the metallic
grid comprises copper or nickel.

5. The method as claimed in claim 2, wherein step (a2) further
comprises:(a21) selecting a plurality of carbon nanotube segments having
a predetermined width from the array of carbon nanotubes; and(a22)
pulling the plurality of carbon nanotube segments at a uniform speed.

6. The method as claimed in claim 5, wherein the carbon nanotube film
comprises a plurality of carbon nanotubes substantially parallel to a
pulling direction.

7. The method as claimed in claim 1, wherein step (c) further comprises
dropping the organic solvent from a dropper to an entire surface of the
carbon nanotube film to make a compact structure between the carbon
nanotube film and the metallic grid.

8. The method as claimed in claim 1, wherein step (c) further comprises
immersing the metallic grid with the carbon nanotube film thereon into a
container having the organic solvent therein, to make a compact structure
between the carbon nanotube film and the metallic grid.

9. The method as claimed in claim 1, wherein the organic solvent comprises
of a material that is selected from the group consisting of ethanol,
methanol, acetone, dichloroethane, and chloroform.

10. The method as claimed in claim 1, further comprising a step of
removing extra portions of the carbon nanotube film on edges of the
metallic grid.

11. A method for making a transmission electron microscope micro-grid, the
method comprising:(a) providing a plurality of carbon nanotube films and
a metallic grid;(b) laying the plurality of carbon nanotube films on the
metallic grid; and(c) treating the plurality of carbon nanotube films on
the metallic grid with an organic solvent.

12. The method as claimed in claim 11, wherein each of the plurality of
carbon nanotube films comprises a plurality of carbon nanotubes
substantially arranged along an aligned direction.

13. The method as claimed in claim 12, wherein the plurality of carbon
nanotube films laid one after another to form a multi-layer carbon
nanotube film structure.

14. The method as claimed in claim 13, wherein the plurality of carbon
nanotube films are stacked to form a microporous structure.

15. The method as claimed in claim 11, wherein step (c) further comprises
dropping the organic solvent from a dropper to an entire surface of the
plurality of carbon nanotube films.

16. The method as claimed in claim 11, wherein step (c) is further
comprises immersing the metallic grid with the plurality of carbon
nanotube films thereon into a container having the organic solvent
therein.

17. A method for making a transmission electron microscope micro-grid, the
method comprising:(a) providing a first carbon nanotube film comprising a
plurality of carbon nanotubes arranged along a first direction, a second
carbon nanotube film comprising a plurality of carbon nanotubes arranged
along a second direction, and a metallic grid;(b) laying the first carbon
nanotube film on the metallic grid;(c) adhering the second carbon
nanotube film on the first carbon nanotube film to form a stacked
multi-layer carbon nanotube film; and(d) treating the stacked multi-layer
carbon nanotube film on the metallic with an organic solvent.

18. The method as claimed in claim 17, wherein in step (c) the second
carbon nanotube film is adhered on the first carbon nanotube film along
such that an angle between the first direction and the second direction
is about 90.degree..

19. The method as claimed in claim 17, wherein step (d) further comprises
dropping the organic solvent from a dropper to soak an entire surface of
the stacked multi-layer carbon nanotube film with the organic solvent.

20. The method as claimed in claim 17, wherein step (d) further comprises
immersing the metallic grid with the stacked multi-layer carbon nanotube
film thereon into a container having the organic solvent therein.

Description:

RELATED APPLICATIONS

[0001]This application is a divisional application of U.S. patent
application, entitled "TRANSMISSION ELECTRON MICROSCOPE MICRO-GRID AND
METHOD FOR MAKING THE SAME" with application Ser. No. 12/005,741, filed
on Dec. 28, 2007. U.S. patent application Ser. No. 12/005,741, claims the
benefit of priority under 35U.S.C. 119 from Chinese Patent Application
200710073768.1 filed on Mar. 30, 2007 in the China Intellectual Property
Office, disclosure of which is incorporated herein by reference.

BACKGROUND

[0002]1. Technical Field

[0003]The present invention relates to a method for making a transmission
electron microscope (TEM) micro-grid.

[0004]2. Discussion of Related Art

[0005]In a transmission electron microscope (TEM), a porous carbon
supporting film (i.e., micro-grid) is used, as an important tool, to
carry powder samples and to observe high-resolution transmission electron
microscope (HRTEM) images. With the development of nano-technology,
micro-grids are increasingly coming into widespread use in the field of
electron microscopy. Recently, the micro-grids used in transmission
electron microscopes are usually manufactured using a layer of organic
porous membrane covered on a metal mesh net, such as copper mesh net, or
nickel mesh net, and subsequently a layer of non-crystal carbon films are
deposited thereon via evaporation.

[0006]However, in actual applications, the non-crystal carbon films
influence the observation of the high-resolution transmission electron
microscopy images significantly, particularly when the diameter of the
observed particles is less than 5 nanometers.

[0007]What is needed, therefore, is a transmission electron microscope
(TEM) micro-grid and method for making the same, and the TEM micro-grids
are conducive to acquiring better high-resolution transmission electron
microscopy images when the diameter of the observed particles is less
than 5 nanometers.

SUMMARY

[0008]In one embodiment, a method for making a TEM micro-grid includes the
steps of: (a) providing an array of carbon nanotubes; (b) drawing a
carbon nanotube film from the array of carbon nanotubes; (c) covering at
least one above-described carbon nanotube film on a metallic grid and
treating the at least one carbon nanotube film with an organic solvent.

[0009]Other advantages and novel features of the present TEM micro-grid
will become more apparent from the following detailed description of
preferred embodiments when taken in conjunction with the accompanying
drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]Many aspects of the embodiments can be better understood with
references to the following drawings. The components in the drawings are
not necessarily drawn to scale, the emphasis instead being placed upon
clearly illustrating the principles of the embodiments. Moreover, in the
drawings, like reference numerals designate corresponding parts
throughout the several views.

[0011]FIG. 1 is a flow chart of a method for making a TEM micro-grid, in
accordance with a present embodiment.

[0012]FIG. 2 is a structural schematic of a TEM micro-grid.

[0013]FIG. 3 shows a Scanning Electron Microscope (SEM) image of a TEM
micro-grid, in accordance with a present embodiment;

[0014]FIG. 4 shows a Scanning Electron Microscope (SEM) image of a carbon
nanotube film of the TEM micro-grid, in accordance with a present
embodiment;

[0015]FIG. 5 shows a Transmission Electron Microscope (TEM) image of gold
nano-particles observed by a TEM adopting a TEM micro-grid in accordance
with the present embodiment.

[0016]FIG. 6 is similar to FIG. 5 but greatly magnified.

[0017]Corresponding reference characters indicate corresponding parts
throughout the several views. The exemplifications set out herein
illustrate at least one preferred embodiment of the present TEM
micro-grid, in at least one form, and such exemplifications are not to be
construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION

[0018]Reference will now be made to the drawings to describe, in detail,
embodiments of the present TEM micro-grid and method for making the same.

[0019]Referring to FIG. 1, a method for making a TEM micro-grid includes
the steps of: (a) providing an array of carbon nanotubes, quite suitably,
providing a super-aligned array of carbon nanotubes; (b) drawing a carbon
nanotube film from the array of carbon nanotubes; (c) covering at least
one above-described carbon nanotube film on a metallic grid, and treating
the at least one carbon nanotube film with an organic solvent.

[0020]In step (a), a given super-aligned array of carbon nanotubes can be
formed by the steps of: (a1) providing a substantially flat and smooth
substrate; (a2) forming a catalyst layer on the substrate; (a3) annealing
the substrate with the catalyst layer thereon in air at a temperature in
an approximate range from 700° C. to 900° C. for about 30
to 90 minutes; (a4) heating the substrate with the catalyst layer thereon
at a temperature in an approximate range from 500° C. to
740° C. in a furnace with a protective gas therein; and (a5)
supplying a carbon source gas to the furnace for about 5 to 30 minutes
and growing a super-aligned array of carbon nanotubes on the substrate.

[0021]In step (a1), the substrate can be a P-type silicon wafer, an N-type
silicon wafer, or a silicon wafer with a film of silicon dioxide thereon.
Preferably, a 4 inch P-type silicon wafer is used as the substrate. In
step (a2), the catalyst can, advantageously, be made of iron (Fe), cobalt
(Co), nickel (Ni), or any alloy thereof.

[0022]In step (a4), the protective gas can, beneficially, be made up of at
least one of nitrogen (N2), ammonia (NH3), and a noble gas. In
step (a5), the carbon source gas can be a hydrocarbon gas, such as
ethylene (C2H4), methane (CH4), acetylene
(C2H2), ethane (C2H6), or any combination thereof.

[0023]The super-aligned array of carbon nanotubes can, opportunely, have a
height of about 200 to 400 microns and includes a plurality of carbon
nanotubes parallel to each other and approximately perpendicular to the
substrate. The super-aligned array of carbon nanotubes formed under the
above conditions is essentially free of impurities, such as carbonaceous
or residual catalyst particles. The carbon nanotubes in the super-aligned
array are closely packed together by the van der Waals attractive force.

[0024]Step (b) further includes the substeps of: (b1) selecting a
plurality of carbon nanotube segments having a predetermined width from
the array of carbon nanotubes; (b2) pulling the carbon nanotube segments
at an even/uniform speed to form the carbon nanotube film.

[0025]In step (b1), quite usefully, the carbon nanotube segments, having a
predetermined width, can be selected by using an adhesive tape as a tool
to contact the super-aligned array. In step (b2), the pulling direction
is, usefully, substantially perpendicular to the growing direction of the
super-aligned array of carbon nanotubes.

[0026]More specifically, during the pulling process, as the initial carbon
nanotube segments are drawn out, other carbon nanotube segments are also
drawn out end to end, due to the van der Waals attractive force between
the ends of adjacent segments. The carbon nanotube film produced in such
manner can be selectively formed having a predetermined width. The carbon
nanotube film includes a plurality of carbon nanotube segments. The
carbon nanotubes in the carbon nanotube film are mainly parallel to the
pulling direction of the carbon nanotube film.

[0027]A width of the carbon nanotube film depends on a size of the carbon
nanotube array. A length of the carbon nanotube film can be arbitrarily
set as desired. In one useful embodiment, when the substrate is a 4 inch
type wafer as in the present embodiment, a width of the carbon nanotube
film is in an approximate range from 1 centimeter to 10 centimeters.

[0028]It is noted that because the carbon nanotubes in the super-aligned
carbon nanotube array have a high purity and a high specific surface
area, the carbon nanotube film is adhesive. As such, the carbon nanotube
film can be adhered to the surface of the substrate directly and a
plurality of carbon nanotube films can be adhered to a surface one after
another to form a multi-layer carbon nanotube film structure. The number
of the layers is arbitrary and depends on the actual needs/use. The
adjacent layers of the carbon nanotube film are combined by van de Waals
attractive force to form a stable multi-layer film.

[0029]Quite usefully, the carbon nanotube film can be treated with an
organic solvent. The organic solvent is volatilizable and can be selected
from the group consisting of ethanol, methanol, acetone, dichloroethane,
chloroform, and combinations thereof. Quite suitably, the organic solvent
is ethanol in the present embodiment. The carbon nanotube film structure
can, beneficially, be treated by either of two methods: dropping the
organic solvent from a dropper to soak the entire surface of side carbon
nanotube film structure or immerging a frame with the carbon nanotube
film structure thereon into a container having an organic solvent
therein. After being soaked by the organic solvent, the carbon nanotube
segments in the carbon nanotube film will at least partially
compact/shrink into carbon nanotube bundles due to the surface tension
created by the organic solvent. Due to the decrease of the surface via
bundling, the coefficient of friction of the carbon nanotube film is
reduced, but the carbon nanotube film maintains high mechanical strength
and toughness. Further, due to the shrinking/compacting of the carbon
nanotube segments into the carbon nanotube bundles, the parallel carbon
nanotube bundles are, relatively, distant (especially compared to the
initial layout of the carbon nanotube segments) to each other in one
layer and cross with the parallel carbon nanotube bundles in each
adjacent layer. As such, a carbon nanotube film having a microporous
structure can thus be formed (i.e., the micropores are defined by the
spacing/gaps between adjacent bundles). The resulting spacing can,
beneficially, be about in a range of 100-500 mesh.

[0030]It is to be understood that the microporous structure is related to
the number of the layers of the carbon nanotube film structure. The
greater the number of layers that are formed in the carbon nanotube film
structure, the greater the number of bundles in the carbon nanotube film
structure will be. Accordingly, the spacing/gaps between adjacent bundles
and the diameter of the micropores will decrease. Further, a carbon
nanotube film structure of arbitrarily chosen width and length can be
formed by piling a plurality of carbon nanotube films and partially
overlapped with each other. The width and length of the carbon nanotube
film structure are not confined by the width and the length of the carbon
nanotube film pulled from the array of carbon nanotubes.

[0031]Step (c) can be executed as follows: (c1) treating at least one
carbon nanotube film achieved by step (b) with an organic solvent; and
(c2) covering the at least one carbon nanotube film on a metallic grid.
In step (c), the material of the metallic grid is copper or other metal
material. The organic solvent is volatilizable and can be selected from
the group consisting of ethanol, methanol, acetone, dichloroethane,
chloroform, and combinations thereof. The organic solvent can be dropped
from a dropper, directly, to soak the entire surface of side carbon
nanotube film structure to make a compact structure between the carbon
nanotube film structure and the metallic grid. After step (c), a step of
removing extra portions of the carbon nanotube film on edges of the
metallic grid is further provided.

[0032]It can be understood that the TEM micro-grid can be made by a carbon
nanotube film drawn from an array of carbon nanotubes covered, directly,
on a metallic grid and a plurality of the carbon nanotube films can be
adhered on the metallic grid with carbon nanotube films thereon in
sequence and parallel to each other. And then, an organic solvent is used
to treat the carbon nanotube films to acquire a TEM micro-grid structure.

[0033]Referring to FIG. 2 and FIG. 3, a TEM micro-grid 20 adopting a
carbon nanotube film structure 24, formed by the method described above,
is shown. The TEM micro-grid 20 includes a metallic grid 22 and a carbon
nanotube film structure 24 covered thereon. The carbon nanotube film
structure 24 includes at least one layer of carbon nanotube film.
Beneficially, the carbon nanotube film structure 24 is formed by a
plurality of carbon nanotube films overlapped or stacked with each other.
The number of the layers and the angle between the aligned directions of
two adjacent layers may be arbitrarily set as desired. A diameter of the
microporous structure relates to the layers of the carbon nanotube film
and is in an approximate range from 1 nanometer to 10 micrometers.

[0034]Referring to FIG. 4, a Scanning Electron Microscope (SEM) image of
the TEM micro-grid adopting multi-layer carbon nanotube films is shown.
The angle between the aligned directions of the stacked multi-layer
carbon nanotube film is 90°. The adjacent layers of the carbon
nanotube film are combined by van de Waals attractive force to form a
stable multi-layer film. The carbon nanotubes in the carbon nanotube film
are aligned. The carbon nanotube film includes a plurality of carbon
nanotube bundles in a preferred orientation. Bundles in two adjacent
layers are crossed with each other to form a microporous structure. A
diameter of the micropores is in an approximate range from 1 nanometer to
10 micrometers.

[0035]The small sizes of the micropores in the microporous structure of
the present embodiment can be used to support nano-materials, such as
nano-particles, nano-wires, nano-rods, for the observation thereof via
TEM. When the size of the nano-particles is less than 5 nanometers, the
effect of the micropores is not obvious, but the adsorption effect of
carbon nanotubes plays a main role. Those nano-particles with small size
can be adsorbed stably on the walls of the carbon nanotubes and can be
observed. Referring to FIG. 5 and FIG. 6, the black particles are gold
nano-particles to be observed. The gold nano-particles are adsorbed
stably on the walls of the carbon nanotubes and that is conducive to the
observation of high-resolution image of gold nano-particles.

[0036]In addition, since the carbon nanotubes in the carbon nanotube array
are of high-purity, uniform size, and have less defects, the TEM
micro-grid of the present embodiment interference to the morphology and
structure of the samples to be observed and the high-resolution image of
the nano-particles adsorbed on the carbon nanotubes is minimized.

[0037]Compared to the conventional TEM micro-grid and method for making
the same, the TEM micro-grid in the present embodiment can be formed by a
carbon nanotube film drawn from an array of carbon nanotubes covered,
directly, on a metallic grid and the method is simple, fast and conducive
to large-scale production. The TEM micro-grid made by the present method
has stable properties. What's more, the absorption property of the carbon
nanotubes is conducive to observation of high-resolution TEM image of
nano-particles with a size of less than 5 nanometers.

[0038]Finally, it is to be understood that the above-described embodiments
are intended to illustrate rather than limit the invention. Variations
may be made to the embodiments without departing from the spirit of the
invention as claimed. The above-described embodiments illustrate the
scope of the invention but do not restrict the scope of the invention.